Uninterruptable Power Supply Systems Flashcards
Many electrical and electronic devices are considered essential to human activities. These devices are called:
Critical Loads
Three key components in a basic UPS system:
The rectifier
The battery
The inverter
UPS System failures are typically due to what three common causes?
Overloading
High temperature
Faulty Inverter
What is often done to accomplish higher reliability in supplying power to critical loads?
Two independent UPS’s are used - a redundant system
Static switches, sometimes called solid state switches can operate in Nano seconds. T or F?
False. They can operate in microseconds
Each solid state contact of a static switch has what devices?
Two thyristors in anti-parallel (reverse paralell) configuration
Basically two SCR’s
What shape waveform does an inverter produce?
Square waveform
Name the three common switches associated with a PWM Inverter:
Which is the default?
SCR’s, IGBT’s, BJT’s
Default is IGBT’s
A PWM Inverter produces a true sinusodial waveform. T or F?
False. It isn’t a true sinusodial
The installation of a UPS system can be divided into what four areas?
Inputs
DC
Outputs
Auxiliaries
Batteries of a UPS can be lead acid or nickel cadmium type. T or F?
False. Can only be lead acid, N.C are not used because they require constant charging and discharging to maintain rated capacity.
As a good practice, you must ensure that the inverter or UPS system output rating is at least ____ % of the maximum critical load demand.
125%
To help prevent short circuits within an Output of an UPS, you should install a high degree of what sort of protection on the critical load wiring?
Mechanical.
Ex: installing cables in conduits
The maintenance bypass switch assembly is made up of three circuit breakers labelled what?
MB -Maintenance Bypass
UIP- UPS Input
UOP - UPS Output
Cool ambient air enters through the bottom of a UPS. T or F?
False. Its the lower part of the UPS air enters from
Why would a UPS have more than one cooling fan installed?
For redundancy, designed for quick replacement without UPS system shutdown.
What would an additional UPS display panel be used to indicate?
Alarms such as high temperature and imminent shutdown warning
What does a higher ambient temperature do to battery cells? And what does a lower ambient temperature do to battery cells?
Higher - rapid chemical deterioration
Lower - reduces battery output capacity
A sealed cell battery has how many years of servicable life?
5 to 10
A vented cell battery has more at 10-15.
What guideline should be followed when doing maintenance on an UPS printed circuit board?
Use an anti-static wristband
What are the three seperate tests of a load transfer test on a UPS system?
Manual transfer test
Simulate a failure in the inverter test
Overload through a dummy load
What sections of a UPS cannot be operated alone for testing purposes?
Inverter
Bypass Switch
A static switch has two SCRS connected in anti-parallel. T or F?
True
All four solid state switches of an inverter on at the same time would equal:
A short circuit condition.
The best method to identify a failed solid state power device is by comparing the dc voltage between the ___________ & ___________ terminals.
Anode & Cathode
True or False:
In 3-phase UPS systems, all line and phase voltages are balanced
True
What is another name for a static switch?
Solid state switch or By-pass
True or False:
There is a noticeable distortion in the waveform during a load transfer of a UPS.
False, though there is a slight distortion at the instant of transfer, it is considered to be negligible.
How many solid state switches are in a basic single-phase PWM inverter? And how are the switches connected?
There are 4, and they are connected in two parallel “totem pole” configurations (basically the same configuration as a bridge rectifier)
How do you calculate instantaneous voltage of a sine wave?
V ᵢₙₛₜₐₙₜₐₙₑₒᵤₛ = Vₚₑₐₖ x sin θ
How do you determine the average voltage of single point of a PWM waveform?
Vavg = Vpeak x (time on/(time on+time off))
